Physics Help Forum Vector-Change in velocity

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 Jan 30th 2009, 09:33 PM #1 Junior Member   Join Date: Jan 2009 Posts: 4 Vector-Change in velocity Hi everyone Just a tad confused: An ice-skater moving at 20m/s turns right through an angle of 60 degrees while maintaining the same speed. What is the magnitude of her change in velocity? The confusing part is how do I draw the triangle to represent this information? Thanks in advance for your help Steven
Jan 30th 2009, 09:47 PM   #2
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 Originally Posted by stevoevo22 Hi everyone Just a tad confused: An ice-skater moving at 20m/s turns right through an angle of 60 degrees while maintaining the same speed. What is the magnitude of her change in velocity? The confusing part is how do I draw the triangle to represent this information? Thanks in advance for your help Steven
A triangle ABC, angle A equals 60 degrees, and AB=AC=60, BC would be the change in velocity. You can use cosine law to find your answer.

 Jan 30th 2009, 09:53 PM #3 Junior Member   Join Date: Jan 2009 Posts: 4 Thanks, that's easy enough (as it is an equilaterla triangle) even though I didn't realise it... Thanks heaps
 Jan 30th 2009, 09:57 PM #4 Junior Member   Join Date: Jan 2009 Posts: 4 Actually just one more thing... Why is the angle 60 degrees, shouldn't it be 120?
Jan 30th 2009, 11:19 PM   #5
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 Originally Posted by stevoevo22 Actually just one more thing... Why is the angle 60 degrees, shouldn't it be 120?
Welcome steven
Which angle are you talking about?
Are you confused why the triangle is equilateral.
It is given that the speed remains same which means the two angles opposite them in the triangle are equal. Now its given that an angle is 60 degree. Then the sum of the other two angles which are equal must be 120 degree. So each must be 60 degree.

 Jan 31st 2009, 01:40 AM #6 Junior Member   Join Date: Jan 2009 Posts: 4 Thanks for the welcome Actually I would like to change that question, because I am no longer confused about that. Instead, I would really like an explanation in simple terms of how the 3rd side of the triangle represents the change in velocity. I understand what the change in velocity is, but I don't understand how this line represents it.
 Feb 4th 2009, 03:12 AM #7 Junior Member   Join Date: Jan 2009 Posts: 9 In simle terms I cannot explain it for velocity but for displacement. See its like this. Suppose you travel 3 m east and then turn 90 degree towards south and travel 4 m (please draw a figure for better understanding). Your displacement (change in position) can be given as the line from your initial position to your final position. This becomes the third side of the triangle. For a right angled triangle you can compute it easily using pythagoras theore. In this case your displacement is 5 m. Similarly you can apply it for velocity. Hope you understood.

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